Project Summary Angiogenesis is one of the hallmarks of cancer and a much-pursued therapeutic target. Most anti-angiogenic agents in clinical use target VEGF, VEGF receptors, or related tyrosine kinases, and have shown significant promise in the neoadjuvant context. However incomplete inhibition, evasive mechanisms, increased metastasis, and the development of resistance have limited long-term success, underscoring the need for a better understanding of the nuances of angiogenic regulation and the identification of new targets for therapy. Recent evidence points to a role for the DNA Damage Repair (DDR) pathway in pathological angiogenesis under conditions of hypoxic stress, as is observed in growing tumors. The DDR pathway is also a recognized promoter of resistance to DNA damaging cancer treatment such as chemotherapy and radiation. Here we propose a novel molecular target, the Eyes Absent protein tyrosine phosphatase (EYA-PTP) to simultaneously target tumor angiogenesis and chemo-resistance. In preliminary studies we have shown that the EYA-PTP activity promotes DDR and angiogenesis, and that inhibition of the EYA-PTP or deletion in host endothelial cells signficantly attenuates tumor growth and angiogenesis. In this project we plan to (1) study the interplay between host endothelial EYA, tumor angiogenesis, and chemo-resistance, and (2) use existing and newly developed EYA-PTP inhibitors as anti-angiogenic and chemosensitzation agents in cell?line based and patient-derived orthoptoic xenografts. The overall impact of this proposal is that it will define a new pathway involved in both tumor angiogenesis, and resistance to DNA damaging first-line therapies. Using both genetic and chemical biology approaches we will have demonstrated that the EYA-PTPs are tractable cancer therapeutic targets.